Electrophotographic materials comprising brominated poly-n-vinyl carbazoles



Jan. 14, 1969 AKlRA |NAM| ET AL 3,421,891

ELECTROPHOTOGRAPHIC MATERIALS COMPRISING BROMINATED POLY-N-VINYL CARBAZOLES Filed June 14, 1965 Po/ymer A Po/ymer B O I Polymer C Sens/WWW Bram/he confem (afom INVENTORS fl/(fra Ihami Kazul'zisa Mar/main yoshinab Muraka rm ATTORNEYS United States Patent 3,421,891 ELECTROPHOTOGRAPHIC MATERIALS COM- PRISING BROMINATED POLY-N-VINYL CAR- BAZOLES Akira Inami, Hirakata-shi, Kazuhisa Morimoto, Osaka,

and Yoshinobu Murakami, Hirakata-shi, Japan, assignors to Matsushita Electric Industrial Co., Ltd., Kadomashi, Osaka, Japan, a corporation of Japan Filed June 14, 1965, Ser. No. 463,612 Claims priority, application Japan, June 18, 1964, 39/314,908, 39/34,910; Oct. 13, 1964, 39/58,871 US. Cl. 96-1.6 11 Claims Int. Cl. G03g 5/00 ABSTRACT OF THE DISCLOSURE This photosensitive material for electrophotography comprises a polymer including recurring units represented by the general formula in which X represents a member selected from hydrogen and bromine, and said polymer is selected from the group consisting of poly-3,6-dibromo-9-vinylcarbazole, copolymers of 3,6-dibromo-9-vinylcarbazole and a vinyl monomer, and brominated poly-9-vinyl carbazole.

This invention relates to photosensitive materials for electrophotography and particularly to the composition of such electrophotographic materials.

The term electrophotography as used in this specification means a reproduction or copying process utilizing a combination of electrostatic and photoconductive phenomena of substances. The conventional silver halide photocopying technique is excellent in sensitivity as well as in resolution and other qualities of copies produced but, because of its chemical and wet-processing nature, is unsatisfactory in speed and controllability of the process and unable to meet the recent demand for highspeed documentary reproduction. These difiiculties can be overcome by the electrophotography which is a dry process including only physical or electrical steps. There are two electrophotographic processes now in practical use: Xerography, which employs a selenium photosensitive plate, and Electrofax, utilizing a resin dispersion of zinc oxide. Other known photosensitive materials for use in electrophotography include inorganic substances such as zinc sulfide and cadmium sulfide and organic substances such as anthracene, anthraquinone, carbazole and perylene, which have long been known. Recently, a group of heterocyclic compounds and a poly-N-vinyl carbazole mixture have been announced by the Kalle Aktiengesellscraft of Germany. The former are disclosed in US. patents, No. 3,041,165, issued June 26, 1962, and No. 3,066,023, issued Nov. 27, 1962, and the latter in US. Patent No. 3,037,861, issued June 5, 1962.

Any of the substances mentioned above are not sufiicient to meet all the requirements including availability, accuracy in use, stability, ease in handling and sensitivity and cannot be considered satisfactory as a modern photocopying material to be used in a large number of fields.

The present invention is concerned with the composition of organic photosensitive materials usable in such electrophotographic processes and provides a novel photosensitive material which is stable in nature having an excellent photosensitivity and which comprises a polymer "ice or copolymer including 3-bromo or 3,6-dibromo 9-vinyl carbazole represented by the general formula where X represents hydrogen or bromine. The electrophotographic material according to the present invention is a high-molecular polymer and has itself a film-forming ability such as to form a homogeneous photosensitive film having a beautiful surface appearance and a very satisfactory resolving power.

If transparent supports are used, the electrophotographic images can also be used as masters for the production of further copies of any sort of light sensitive sheets.

The present invention is based upon the finding that an electrophotographic material advantageously usable in a variety of electrophotographic processes can be obtained by employing a polymeric substance including recurring units represented by the above general formula to make electrophotographic layers. Polymers employed in the present invention are all novel substances which find no mention in literatures. Description will now be made on the methods of synthetizing the respective substances.

(1) Synthesis of 3,6-dibromo-9-vinyl carbazole Twelve grams of 9-B-chloroethyl carbazole is partly dissolved in 200 ml. of glacial acetic acid. To this solution is added a solution of 8 g. of potassium bromide in 16 ml. of water. At room temperature, 12 g. of potassium bromate is added to the mixture in 30 minutes while stirring the latter. After stirring for 3 hours at 30 C., the mixture solution is poured in iced water, left to stand overnight and then filtered to separate out 17 g. of crude product. The product was recrystallized twice from methanol and twice from ligroin to obtain 14.5 g. of 3,6- dibromo-9-fl-chloroethyl carbazole in the form of white need-1e crystals having a melting point of 156 to 157 C. The yield was approximately 71%. Two grams of the substance was dissolved in 60 ml. of ethanol and to the solution was added 40 ml. of 25% potassium hydroxide solution in methanol. After refluxing for 2.5 hours the mixture was poured into iced water, left to stand overnight and filtered off. The filtered product was recrystallized twice from n-hexane to obtain 1.3 g. of white needle crystals at the yield of 74%. The crystalline substance obtained exhibited a melting point of 74 to 75 C. and its composition, upon elementary analysis, was: C, 48.16%; H, 2.77%; N, 4.34% and Br, 45.00%, which closely approximate the calculated values upon the basis of its formula, C H NBr C, 47.86%; H, 2.56%; N, 3.99% and Br 45.58%.

As for the benzene-ring out-of-plane vibrations of the hydrogen atom in the infrared absorption spectrum, the substance does not absorb at the characteristic absorption bands of 725 and 747 cm. of 1,2-di-substituted ring and strongly absorbs at the characteristic absorption band of 800 cm? of 1,2,4-tri-substituted ring. This reveals that the substance obtained is 3,6-dibromo-9-vinyl carbazole.

(2) Polymerization of 3,6-dibromo-9-vinyl carbazole This substance can be polymerized by any of previously known techniques including radical and thermal polymerization methods. For example, 5 g. of monomer is placed in a tube and the air therein is substituted by nitrogen gas. Subsequently the tube is sealed and heated at C. for 3 hours. The sample is then dissolved in tetrahydrofuran and thrown into alcohol to obtain a white polymer. The yield of the polymer was 3.5 g. and it exhibited an intrinsic viscosity of 0.10 as measured in dimethyl formamide at C. The polymer is soluble in tetrahydrofuran, dioxane, dimethyl formamide, chlorobenzene and nitrobenzene.

(3) Copolymerization of 3,6-dibromo-9-vinyl carbazole 3,6-dibromo-9-vinyl carbazole can be copolymerized with other vinyl monomers by any of known techniques including radical and thermal polymerization methods. Monomers usable for copolymerization include styrene, vinyl naphthalene, vinyl anthracene and vinyl carbazole. For example 2 g. of 3,6-dibromo-9-vinyl carbazole and 2 g. of 9-vinyl carbazole are placed in a tube and the air therein is substituted by nitrogen gas. Then after the tube is sealed, the mixture is heated for polymerization for 3 hours and thrown into alcohol to obtain a white polymer. Its yield was 3 g. and its intrinsic viscosity as obtained at 30 C. in dimethyl formamide was 0.13. The ratio of copolymerization obtained from elementary analysis was 56.9 mole percent of 3,6-dibromo-9-vinyl carbazole. This copolymer is soluble in chlorobenzene, nitrobenzene, dimethyl formamide and tetrahydrofuran. When used as an electro-photographic material, it has been found that the copolymer of 3,6-dibromo-9-vinyl carbazole and 9-vinyl carbazole, including 25 mole percent or more of 3,6-dibromo-9-vinyl carbazole, has a sensitivity approximately five times as high as that of poly-9-vinyl carbazole, as shown in the accompanying drawing. 1n the case of the copolymer of 3,6-dibromo-9- vinyl carbazole with styrene or l-vinyl naphthalene, it has been found that the 3,6-dibromo-9-vinyl carbazole content of mole percent or over gives satisfactory results.

The polymer including bromine-substituted 9-vinyl carbazole units according to the present invention can also be obtained by the following bromination method distinct from the above-described processes. The bromination reaction is highly characterized in that bromine used in the reaction is added to poly-9-vinyl carbazole in a quantitative fashion and thus any brominated compound can be obtained with ease by the reaction. Experiments have shown that it is possible to add at most two bromine atoms to each carbazole unit and, as revealed by infrared spectrophotometry, at its 3- or 3,6-positi0ns. The polymer thus obtained is white in color and soluble in chlorobenzene, dioxane, dimethyl formamide and nitrobenzene.

A few examples of the bromination method will next be described.

(1) Twenty grams of po1y-9-vinyl carbazole (registered tradename Luvican M-170) is dissolved in 450 ml. of chlorobenzene and to the solution are added 18.44 g. of N-bromo succiniznide and 0.173 g. of benzoyl peroxide. The mixture is heated at 80 C. for 2 hours While being stirred thoroughly. Then the reactant is thrown into methanol to obtain a white polymer, which is dissolved in chlorobenzene and again thrown into methanol for purification. The pure polymer thus obtained as a precipitate exhibited upon elementary analysis a halogen value of 29.87%, which approximates the value calculated, 29.44%, of the monobromo substituted product from poly-9-vinyl carbazole. This reveals that the polymer obtained is a monobromo substituted product.

(2) Twenty grams of poly-9-vinyl carbazole is dissolved in 450 ml. of benzene, and 9.22 g. of N-bromosuccinirnide and 0.087 g. of benzoyl peroxide are added. The mixture is heated at 80 C. for 2 hours while being stirred thoroughly. Then the reactant is thrown into methanol to obtain a White polymer, which is dissolved in benzene and thrown again into methanol for purification. The polymer thus purified exhibited upon elementary analysis a halogen value of 17.05%, which approxi- Bromination of poly-9-vinyl carbazole mates the value calculated, 17.22%, of the half bromo substituted product from poly-9-vinyl carbazole. This reveals that the polymer includes one bromine atom as a substituent for each two carbazole units.

To use the polymer obtained by any of the methods described above as an electrophotographic material, a solution including the following ingredients is prepared and coated on an appropriate supporting medium and dried:

(1) Photoconductor (prepared according to the above examples),

(2) Sensitizer,

(3) Chemical sensitizer,

(4) Plasticizer.

As the case may be, any of the last three ingredients can be omitted.

Sensitizer As a sensitizer, commercially available dyestuffs are usable. By adding such dyestutf the photosensitivity region of the photoconductor is shifted to the light-absorbing region or the visible ray region of the dyestutf to exhibit a satisfactory sensitivity even in the visible range of light wavelength. Examples of such dyestulf include brilliant green, methyl, violet, crystal violet, rhodamine B, rhodamine B extra, rhodamine 6G, sulphorhodamine B, rose bengal, methylene blue, and alixarine. Among these methylene blue and crystal violet are highly effective. The amount of dycstult added is from 0.01 to 2.0% by weight.

Chemical sensitizer Aromatic quinones, halogenated aromatic compounds, acid anhydrides and cyano compounds have highly favorable etiects upon the photo-conductivity of the photoconductor according to the present invention by forming together therewith a charge-transfer complex. Aromatic quinones usable as a chemical sensitizer are p-benzoquinone, 1,2-benzanthraquinone, anthraquinone, naphthoquinone, 2-methyl anthraquinone, 2-chloroanthraquinone, 1-nitroanthraquinone, 2-nitroanthraquinone, etc. Acid anhydrides usable include maleic anhydride, phthalic anhydridc, succinic anhydride, etc. Recommendable cyano compounds are tetracyanoethylene, tetracyanoquinodimethane, etc. Any of the compounds mentioned above is added to the above polymer in an amount of from 1 to 25 weight percent and preferably from 1 to 7 weight percent. Among others, addition of l-nitroanthraquinonc or Z-methylanthraquinone is very effective.

Plasticizer The polymers described above have a film-forming ability by themselves but, when desired, an appropriate plasticizer may be added to the polymer in an amount of 5 to by weight of it for the purpose of further improving the properties of the photosensitive layer formed with the polymer. Usable as such plasticizer are p-terphenyl, diphenyl, diphenyl ether, chlorinated diphenyl, methyl naphthalene, chlorinated aliphatic acid ester, dioctyl phthalate, triphenyl phosphate, dimcthylglycol phthalate, dibutyl phthalate, chloroparaffin. epoxy resin (of the registered tradename Epon 828"), and others. Polycarbonate resin is completely compatible with the photoconductive polymer of the present invention and very effective to improve the film strength and electrostatic characteristics of the polymer.

As a support or backing material, zinc, silver or other metal sheeting, paper surface-treated as with synthetic resin to prevent impregnation of the material coated, synthetic resin film treated with an antistatic agent to reduce its electric resistivity, synthetic resin film having an electric resistivity two or three orders lower than that of the photoconductor layer, synthetic resin film vacuum-deposited with metal or copper iodide, glass sheet, etc., are utilizable.

For coating the polymer, any known method of forming a film of synthetic resin may be followed. For example, the film may be formed by the flushing, rotational coating, spraying or brushing of the polymer solution and the photosensitive layer thus formed can have any adjusted thickness ranging from 2 to 30 according to the respective purposes.

For formation of electrophotographic images, any known technique may be followed employing either positive or negative charges for a corona discharge of the photosensitive layer. For example, positive charges may be accumulated on the photosensitive surface by passing thelayer several times below a 6 kv. corona-discharging device in a darkness until the surface potential reaches a value of 300 to 900 volts. An appropriate light source, for example, a tungsten lamp is used to shed light on the film through a proper positive pattern and thus the charges on the exposed area of the film are neutralized. Subsequently, a negatively charged developing powder known as toner is sprinkled to obtain a positive image, which can be fixed by light heating or passing through an appropriate solvent vapor. Instead of using a toner, any suitable liquid-developing method may also be employed.

Description will next be made on the effect of 3-bromo- 9-vinyl carbazole units or 3,6-dibromo-9-vinyl carbazole units upon the electrophotographic sensitivity with reference to the accompanying drawing. In the following description, measurement of the sensitivity has been made according to the method disclosed in the Bulletin of the Chemical Society of Japan, vol. 37, No. 6, pages 842-844 (by A. Inami et al.). The sensitivity in the drying is defined as a half-decay-exposure in lux-second unit, said exposure is the exposure to reduce a surface potential of a photosensitive layer to a half of the surface potential in the dark. The smaller half-decay-exposure represents a higher sensitivity. In the graphical illustration of the drawing, polymer A represents poly-3,6-dibromo- 9-vinyl carbazole as obtained by the above synthetizing method (2); polymer B represents the copolymer of 3,6- dibromo-9-vinyl carbazole and 9-vinyl carbazole as o'b tained by the method (3) in different copolymerization ratios; and polymer C represents the brominated poly-9- vinyl carbazole as obtained by the method (4) in different degrees of bromination. The ordinate represents the sensitivity of the polymers A, B and C while the abscissa represents the number of bromine atoms substitutul in the nucleus.

As seen from the illustration, the brominated carbazole ring has a considerably increased effect upon the sensitivity of the product. Polymer C is considered to be a mixture of carbazole, its 3-position substitution product and 3,6-position substitution product, and this supposedly accounts for the difference in sensitivity between polymers B and C.

Some practical examples of the present invention will next be described.

EXAMPLE 1 One gram of poly-3,6-dibromo-9-vinyl carbazole is dissolved in ml. of tetrahydrofuran and this solution is applied by the rotational coating method to an aluminum sheet so that the coated film after drying has a thickness of approximately 3a. In a conventional manner, negative charges are deposited on the coated film by means of a corona-discharging device set at about 6 kv. and then the film is placed under a positive original and exposed therethrough for 7 seconds to a light illumination of 1000 luxes. Subsequently, an image true to the original is obtained by the sprinkling of a toner and fixed by slight heating.

EXAMPLE 2 One gram of poly-3,6-dibromo-9-vinyl carbazole is dissolved in 10 ml. of tetra-hydrofuran and 0.3 g. of diphenyl chloride and 0.1 g. of 2-methylanthraquinone are added. This solution is applied to paper to form a layer approximately 5 1. thick when dried. In the conventional manner, the layer is exposed for 2 seconds to an illumination of -lux intensity to obtain an image true to the original.

EXAMPLE 3 A solution of 1 g. of poly-3,6-dibrom-o-9-vinyl carbazole in 10 ml. of tetrahydrofuran is prepared and to it are added 0.3 g. of chlorinated diphenyl, 0.12 g. of Z-methyl anthraquinone, and 5 mg. of crystal violet. The solution is applied to paper to form a layer approximately 5,41. thick when dried. The layer is then exposed to illumination of 100 luxes for 0.5 second and an image true to the original is obtained by use of a toner powder.

EXAMPLE 4 One gram of copolymer of 3,6dibromo-9-vinyl carbazole and styrene (containing the former in 70 mole percent) and 0.1 g. of 2-methyl anthraquinone are dissolved in 10 ml. of benzene. The solution is applied to an aluminum sheet by the rotational coating method to obtain a layer approximately 2;; thick when dried. Positive charges are given to the film conventionally by the corona discharging at approximately 6 kv. and subsequently the film laid under a positive original is subjccted to light" exposure of 1000 luxes for 2 seconds. An image true to the original is obtained by sprinkling a toner powder over the film exposed and is fixed by slight heating.

EXAMPLE 5 One gram of copolymer of 3,6-dibromo-9-vinyl carbazole and 9-viny1 carbazole (containing the former in 65 mole percent, 0.15 g. of 2-methyl anthraquinone, 0.3 g. of diphenyl chloride and 1 mg. of crystal violet are dissolved in 10 ml. of tetrahydrofuran. This solution is applied to paper to obtain a layer 5, thick when dried. The film is conventionally subjected to a light exposure of 100 luxes for 0.5 second to Obtain an image true to the original.

EXAMPLE 6 One gram of copolymer of 3,6-dibromo-9-vinyl carbazole and l-vinyl naphthalene (containing the former in 78 mole percent is dissolved in 10 ml. of chlorobenzene and to the solution are added 0.2 g. of tetracyanoethylene and 0.2 g. of methylnaphthalene. The resulting solution is applied to paper to obtain thereon a film 5a thick when dried. The layer is conventionally subjected to a light exposure of 100 luxes for a single second to obtain an image true to the original.

EXAMPLE 7 One gram of brominated poly-9-vinyl carbazole (degree of bromination 78 mole percent) is dissolved in 10 ml. of chlorobenzene and 0.2 g. of methylnaphthalene is added. The film layer formed by coating the solution and dried is subjected to corona discharging at approximately 9 kv. to be charged positively and under a positive original is exposed to light from a tungsten lamp for 10 seconds maintaining the intensity of illumination 0n the surface of the photosensitive layer at 1000 luxes. In the well known manner, a toner powder is sprinkled on the layer to obtain an image true to the original. In case a photosensitive liquid of the same composition as that described above and prepared from poly-9-vinyl carbazole is coated, it has been found that an exposure time of 40 seconds is required.

EXAMPLE 8 One gram of brominated poly-9-vinyl carbazole (degree of bromination mole percent) is dissolved in 10 ml. of chlorobenzene, and 0.5 g. of chlorinated diphenyl, 0.1 g. of Z-methyl anthraquinone and 1 mg. of crystal violet are added. By the conventional method, the solution thus prepared is applied to an aluminum sheet to form a film coating, which is charged and subjected to an exposure of 100 luxes for 0.5 second. By sprinkling a toner powder on the film, an image true to the original is obtained.

EXAMPLE 9 One gram of brominated poly-9-viny1 carbazole (degree of bromination 150 mole percent) is dissolved in 10 ml. of chlorobenzene and to the solution are added 0.3 g. of chlorinated paratfin, 0.05 g. of 2-nitroanthraquinone and 0.5 mg. of methylene blue. The resulting solution is applied to a film of polyethylene terephthalate vacuumdeposited with copper iodide to obtain a sensitive layer 101.0 thick when dried. Following the same procedure as in Example 8, an image true to the original is obtained with an exposure time of one second.

EXAMPLE 10 One gram of brominated poly-9-vinyl carbazole (degree of bromination 100 mole percent) is dissolved in 10 ml. of chlorobenzene and to the solution are added 0.1 g. of chlorinated aliphatic acid ester (of the registered tradename Adecasizer S3"), 0.2 g. of epoxy resin (of the registered tradename Epon 828), 0.5 g. of polycarbonate resin (of the registered tradename Panlite-C), 0.05 g. of l-nitroanthraquinone and 0.1 mg. of methylene blue. This preparation is applied to a film of cellulose triacetate with copper iodide vacuum-deposited thereon to form a layer having a dry thickness of 10 The layer is negatively charged and then subjected to a light exposure of 100 luxes for 0.5 second. An image true to the original is developed by sprinkling a toner on the exposed layer and fixed by heating it slightly.

As will be apparent from the foregoing description, the present invention provides a photosensitive material for electrophotography use which is entirely novel comprising a polymer including recurring units represented by the general formula l err-en?- where X represents hydrogen or bromine atom. It will be appreciated that the photosensitive material of the present invention has a sensitivity comparable to that previously obtainable with inorganic substances such as zinc oxide and selenium and, when laminated on a transparent support, gives a light-transmitting photographic material.

Also, it has been found that the material of the present invention exhibits a high adhesive strength to its support and is never separated therefrom even if the latter is subjected to bending or other external forces. Also, since the material is a high molecular polymer having itself a high film-forming ability, it is apparent that it can form photosensitive films which are homogeneous, beautiful in external appearance and thus very satisfactory in resolving power and other qualities required for successful electrophotographic copying.

The term polymer as used in this specification and the appended claims should be construed to mean either homopolymer or copolymer.

8 What is claimed is: 1. A photosensitive material for electrophotography comprised of a polymer including recurring units represented by the general formula CH-CII2 in which X represents a member selected from hydrogen and bromine.

2. A photosensitive material for electrophotography according to claim 1 comprised of polymerized 3,6- dibromo-9-viny1 carbazole.

3. A photosensitive material for electrophotography according to claim 1 comprised of copolymers of 3,6- dibromo-9-vinyl carbazole and a vinyl monomer.

4. A photosensitive material for electrophotography according to claim 1 comprised of a copolymer of 3,6- dibromo-9-vinyl carbazole and styrene.

5. A photosensitive material for electrophotography according to claim 1 comprised of a copolymer of 3,6- dibromo-9-vinyl carbazole and 9-vinyl carbazole.

6. A photosensitive material for electrophotography according to claim 1 comprised of a coplymer of 3,6- dibromo-9-vinyl carbazole and l-vinyl naphthalene.

7. A photosensitive material for electrophotography according to claim 1 comprised of a polymer formed by the bromination of poly-9-vinyl carbazole.

8. A photosensitive material for electrophotography according to claim 1 comprised of poly-9-vinyl carbazole brominated with N-bromo-succinimide using benzoyl peroxide as a catalyst.

9. A method of improving the sensitivity of a material as claimed in claim 1 by adding to the material a sensitizer selected from the group consisting of methylene blue and crystal violet.

10. A method of improving the sensitivity of a material as claimed in claim 1 by adding to the material a chemical sensitizer selected from the group consisting of Z-methylainthraquinone and Z-nitroanthraquinone.

11. A method of improving the strength and the flexibility of a photosensitive layer formed of a material as claimed in claim 1 by adding to the material a plasticizer selected from the group consisting of chlorinated diphenyl, methyl naphthalene, chlorinated aliphatic acid ester, epoxy resin and polycarbonate resin.

References Cited UNITED STATES PATENTS 3,037,861 6/1962 Hoegl et al 96-4 3,155,503 11/1964 Cassiers et a1. 96-1 3,240,594 3/1966 Cassiers et a1. 96-l. 3,307,940 3/1967 Hoegl et al 96-1 3,341,472 9/1967 Hewett 250-501 J. TRAVIS BROWN, Primary Examiner.

JOHN C. COOPER, III, Assistant Examiner.

US. Cl. X.R. 96-1.5; 26088.3 

